1. Field of the Invention
This invention relates to sulfonyldiazomethane compounds suited for chemical amplification resist materials for the fabrication of integrated circuits or the other electronic devices which are sensitive to radiation such as UV, deep UV, electron beams, x-rays, excimer laser beam, γ-rays, and synchrotron radiation; photoacid generators for resist materials; and resist materials comprising the sulfonyldiazomethane, and a patterning process using the material.
2. Description of the Related Art
As a finer pattern rule is requested in the trend of higher integration and higher speed of LSI, deep-ultraviolet lithography is regarded promising as a microfabrication technology of next generation.
In recent days, technology making use of, as a deep UV light source, a high-luminosity KrF excimer laser, especially an Ar F excimer laser featuring a shorter wavelength has attracted attentions. In order to deal with a decrease in the wavelength of an exposure light and heightening in the resolution of a resist material, there is a demand for the development of more improved microfabrication technology.
From such viewpoints, chemical amplification resist materials which have been developed recently and employ an acid as a catalyst are particularly promising resist materials for deep UV lithography, because they have excellent features such as high sensitivity, resolution and dry etching resistance. The chemical amplification resist materials can be classified into positive type in which unexposed areas remain by the removal of exposed areas and negative type in which the exposed areas remain by the removal of unexposed areas.
In chemical amplification positive resist materials to be developed with an alkaline developer, a resin and/or compound have part or all of the alkali soluble phenol or carboxylic acid protected with a substituent (acid-labile group) capable of changing the solubility of the resin and/or compound in an alkali developer by the action of an acid. It is catalytically decomposed by an acid generated upon exposure and the exposed area on which phenol or carboxylic acid has been generated is removed by the alkaline developer. In chemical amplification negative resist materials, a resin and/or compound having an alkali-soluble phenol or carboxylic acid and a compound (acid crosslinking agent) capable of bonding (crosslinking) the resin or compound under the action of an acid are crosslinked by an acid generated upon exposure, whereby the exposed area is made insoluble in the alkali developer and the unexposed area is removed by the alkaline developer.
In the chemical amplification positive resist materials, a resist film is formed by dissolving a binder resin having an acid-labile group and a compound capable of generating an acid upon exposure to radiation (which will hereinafter be referred to as “photoacid generator”) in a solvent, applying the resultant resist solution onto a substrate by any one of a variety of methods, heating if necessary, and evaporating off the solvent. The resist film is then exposed to radiation, for example, deep UV as a light source through a predetermined mask pattern. The exposed resist film is then optionally subjected to post exposure bake (PEB) in order to promote catalytic reaction with an acid, followed by development with an aqueous alkaline solution to remove the resist film from the exposed area, whereby a positive pattern profile is obtained. After the substrate is etched by any one of various methods, the remaining resist film is removed by dissolution in a remover solution or ashing to form a desired pattern profile on the substrate.
For the chemical amplification positive resist materials for KrF excimer laser, a phenolic resin such as polyhydroxystyrene having part or all of the hydrogen atoms of the phenolic hydroxyl groups protected with an acid-labile protective group have been used. As the photoacid generator, iodonium salt, sulfonium salt, or bissulfonyldiazomethane has been used. If necessary, a carboxylic acid and/or phenol derivative having a molecular weight not greater than 3,000 and having part or all of the carboxylic acid and/or phenolic hydroxyl groups protected with an acid-labile group, which serves as a dissolution inhibiting or promoting compound; a carboxylic acid compound for improving dissolution properties; a basic compound for improving contrast; and a surfactant for improving application properties are added.
Bissulfonyldiazomethanes as shown below are suited for use as a photoacid generator of chemical amplification resist materials, especially chemical amplification positive resist materials for KrF excimer laser, because they are excellent in sensitivity and resolution, and are superior in compatibility with resins and solubility in resist solvents over sulfonium salt or iodonium salt photoacid generators, as disclosed in Japanese Patent No. 3024621 or Japanese Patent Application Unexamined Publication No. 3-103854/1991.

Sulfonyldiazomethanes having aryl groups, however, show a large absorption in a deep UV wavelength region and a high content thereof lowers transparency of the resist film itself, leading to deterioration in the pattern shape. When a diazomethane having the alkyl group instead of the aryl group is used, an acid having a relatively low molecular weight is generated, which tends to lower resolution owing to a large diffusion of it in the resist film. When it is added in a larger amount, the problem of an insoluble matter upon development and/or removal of the resist film cannot be overcome owing to the high crystallinity of the compound itself.
The positive resist material comprising a disulfonyldiazomethane having an acid-labile group such as tert-butoxycarbonyloxy group, ethoxyethyl group or tetrahydropyranyl group in order to improve contrast is also proposed in Japanese Patent Application Unexamined Publication No. 10-90884/1998. According to the investigation by the present inventors, however, such a compound lacks stability.
The present inventors have already synthesized a sulfonyldiazomethane having an acyl group such as acetyl or a methanesulfonyl group introduced therein and used it as a photoacid generator of a chemical amplification resist material. The acyl or methanesulfonyl-substituted arylsulfonyldiazomethane, however, lacks stability under basic conditions. Moreover, their absorption in the deep UV is strong owing to the aryl group in the molecule so that addition of a large amount thereof lowers transparency of the resist film itself (Japanese Patent-Application Unexamined Publication Nos. 2001-55373 and 2001-106669).
Combination of two or more photoacid generators for a resist material is a technique already disclosed in Japanese Patent Application Unexamined Publication No. 8-123032/1996. It is reported in Japanese Patent Application Unexamined Publication No. 11-72921/1999 that incorporation of a radiation-sensitive photoacid generator comprising a mixture of a compound which generates a three-or-more-fluorine-containing sulfonic acid by exposure to radiation and a compound which generates a fluorine-free sulfonic acid by exposure to radiation improves resolution without causing nano edge roughness or film surface roughness; or in Japanese Patent Application Unexamined Publication No. 11-38604/1999 that a resist material comprising an asymmetric bissulfonyldiazomethane such as a bissulfonyldiazomethane having alkylsulfonyl and arylsulfonyl groups or a bissulfonyldiazomethane having arylsulfonyl and alkoxy-substituted arylsulfonyl groups, and a polymer of a polyhydroxystyrene derivative having an acid-labile group has resolution at least equal to conventional materials, a sufficient sensitivity and significantly excellent heat resistance. According to the investigation by the present inventors, however, these resist materials are unsatisfactory in resolution and from the synthetic and industrial standpoints, asymmetric bissulfonyldiazomethanes have drawbacks.
When the time from exposure to post-exposure baking (PEB) (PED: post-exposure delay) is prolonged, a change in pattern profile tends to occur. In a chemical amplification positive resist material using an acid-labile group such as acetal, it appears as a thinned line width of unexposed areas, while in a chemical amplification positive resist material using an acid-labile group such as tert-butoxycarbonyl (t-BOC), it appears as a thickened line width of unexposed areas. The period from exposure to PEB is sometimes prolonged for the operational reason so that there is a demand for stable resist materials not causing such a change, that is, a resist material having good PED stability.
The solubility of a photosensitizing agent or photoacid generator has been regarded as a problem since quinonediazide was used as a photosensitizing agent for non-chemical amplification resist materials. More specifically, the problems involve the solubility of a photoacid generator in resist solvent, the compatibility between the photoacid generator and resin, the solubility in (or affinity with) a developer of photo-decomposed products and the photo-undecomposed compound (photoacid generator) after exposure and PEB, and the solubility of the photoacid generator in a remover solvent upon resist removal (peeling). Poor solubility presumably causes precipitation of the photoacid generator during storage, difficulty in filtration, uneven coating, striation, abnormal resist sensitivity, and appearance of foreign matters, dissolution residues or stains on the pattern or in the space after development.